Fog reduction in silver halide emulsions with a diphenyldisulfide dicarboxylic acid



United States Patent F 0G REDUCTION IN SILVER HALIDE EMULSIONS WITH A DIPHENYLDISULFIDE DICARBOXYLIC ACID Fritz Derseh and Charles A. Clark, Binghamton, N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed May 16, 1963, Ser. No. 281,054

19 Claims. (Cl. 96-61) This invention relates to photographic materials and to methods for preparing them. More particularly it relates to light-sensitive silver halide emulsions contain ing compounds which serve as stabilizing and antifogging agents.

It is known in photographic art that light-sensitive gelatino silver halide emulsions have a tendency to fog for example, upon prolonged ripening of the emulsions,

prolonged storage of film or paper bearing the emulsion especially at elevated temperature and humidityand upon prolonged development. The tendency to fog is especially pronounced in rapid development processes carried out at elevated temperatures.

A great number of chemical compounds have been described in the prior art as effective to reduce fog in lightsensitive silver halide emulsions, thus increasing their stability. However, most of these copounds are inadequate when the film or paper bearing the emulsion is subjected to rapid development at elevated temperatures. Moreover, many of the stabilizers and antifogging agents of the prior art have the disadvantage of causing decreased sensitivity, resulting in loss of speed and/or contrast of the emulsion when developed.

It is accordingly a primary object of this invention to produce light-sensitive silver halide emulsion containing stabilizing and fog inhibiting agents which do not appreciably lower the sensitivity of the emulsion.

A further object of the invention is to provide lightsensitive silver halide emulsions which do not develop excessive fog during rapid development at elevated temperatures.

We have discovered that the above objects can be accomplished by adding to the light-sensitive silver halide emulsion a diphenyldisulfide dicarboxylic acid of the following general formula:

COOH (IJOOH wherein the disulfide group occupies any one of the positions ortho, meta, and para to the carboxyl groups.

Diphenyldisulfide-3,3-dicarboxylic acid can be prepared by adding 35 g. of zinc dust in small portions over a period of six hours to a solution of 20 g. of m-chlorosulfonyl benzoic acid in 150 ml. of ethanol and 100 ml. of concentrated hydrochloric acid while agitating the mixture, filtering out undissolved zinc and zinc salts, mixing the filtrate with solid ferric chloride to precipitate the disulfide in crystalline form, recovering the latter product by filtering, washing successively with water and acetone, and finally re-crystallizing from glacial acetic acid. The resulting product consists of cream colored needles having a melting point of 246 C.

References to the preparation of the corresponding ortho and para isomers are given in Beilstein: Handbuch der Organischen Chemie (Fourth Edition), vol. X, page 129; ibid.vol. X (2nd supplement), page 111.

The antifogging agents of the invention may be added to the emulsion at any stage during its process of production. Thus, they may be added as a ripening final" or as a coating final. When added as a ripening final, they are added during the ripening or sensitivity-increasing stage of the emulsion-making process. Such addition may be made before, during or after the addition of a soluble silver salt to the soluble halide in the presence of a suitable colloid, such as gelatin, polyvinyl alcohol, solubilized casein or albumin. When added as a coating final, the antifogging agents of the invention are added to the emulsion just prior to coating it on a suitable support such as glass, paper, or film at a time when the emulsion has nearly attained its maximum sensitivity.

In some instances it is advantageous to apply the antifogging and stabilizing compounds of the invention in a separate layer such as an undercoating or in an antiabrasion gelatin surface layer. In some cases it is desirable to incorporate the compounds in one or all processing baths for the light-sensitive material such as the developer solution, or the preand post-baths.

When used as a ripening final, the antifoggants of this invention are preferably added to the emulsion in an amount ranging from 0.02 to 5 mg. per 0.6 gram-moi of silver halide; and when used as a coating final they are preferably added in an amount ranging from 1 to 20 mg. per 0.6 gram-moi of silver halide. In many emulsions, it is preferable to apply the antifoggants for best effectiveness in a gelatin surface coating. The optimum amount depends primarily on the type of emulsion which is used and should be determined individually in each case.

The stabilizers and antifoggants of the invention may also be used in combination with other known antifoggants and stabilizers, and also in combination with sensitizers such as sulfur-, reduction-, metaland noble metal sensitizers as well as in combination with speed-increasing agents and accelerators such as polyoxyalkylenes and their derivatives.

The antifoggants and stabilizers of the invention may be used with various types of photographic emulsions such as non-sensitized, orthochromatic, panchromatic and X-ray emulsions, paper emulsions and color emulsions.

The following examples, wherein parts and percentages are by weight unless otherwise indicated, are given as an illustration of the manner in which the antifoggants of this invention can be used. It is to be understood however that the examples are given by way of illustration and not by way of limitation.

Example I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was prepared in a conventional manner and brought up to its maximum lightsensitivity. It was then readied for coating, finals were added such as sensitizing dyes and hardening agents and a 0.1% solution of diphenyldisulfide-3,3'-dicarboxylic acid was added in varying amounts to samples of the emulsion as an antifoggant and stabilizer The emulsion samples contained about 0.6 gram-moi of silver halide. The thus prepared emulsion samples Were coated on a cellulose ester film base and dried. Samples of the film thus coated Were then exposed in a type IB sensitometer and developed in a developer having the following composition:

Metol 1.5 Sodium sulfite (anhydrous) 45 Sodium bisulfite 1 Hydroquinone 3 Sodium carbonate (monohydrate) 6 Potassium bromide 0.8

Water to make one liter.

The developed samples were short-stopped, fixed, washed and dried. The results were as follows:

Exposed samples of photographic film were developed for 12 minutes at 65 F. in a standard Metol-hydroquinone developer. Two tests were made-one with normal developing solution, as aforesaid, and one with the same developer composition to which 4 mg. of diphenyldisulfide-3,3-dicarboxylic acid were added per liter. Sensitometric strips developed for 12 minutes in the normal developer as a control showed a fog of 0.36 while those developed in the same developer containing the antifoggant of this invention had a fog of 0.15.

Example III A gelatin-silver halide emulsion containing 2% silver iodide and 98% silver bromide was coated on a film base in a manner known to the art. After coating, an aqueous gelatin solution containing g. of gelatin and 50 mg. of diphenyldisulfide-3,3-dicarboxylic acid in one liter of water was coated on the face of the emulsion as an antiabrasion layer. After drying, film samples were exposed and processed as described in Example I, except that the development was carried out at a temperature of 115 F. Control samples containing no anti-abrasion coating, as above described, developed a fog of 0.23, while the sample containing the antifoggant of the invention in the anti-abrasive coating developed a fog of 0.13. No speed loss was encountered.

Similar results are obtained when development was carried out at temperatures ranging from 95 F. to 120 F.

Results similar to those set out in the examples are obtained upon substitution for the diphenyldisulfide-3,3'- dicarboxylic acid employed therein, of corresponding amounts of diphenyldisulfide-2,2-or 4,4 dicarboxylic acid.

The invention is not limited to the detailed description contained herein, but includes modifications within the scope of the appended claims.

We claim:

1. A light-sensitive silver halide emulsion containing as an antifogging and stabilizing agent a compound of the following general formula:

(300E (IJOOH wherein the disulfide radical occupies one of the positions ortho, meta and para to the carboxyl group in each of the benzene rings.

2. A light-sensitive silver halide emulsion as defined in claim I wherein the antifogging and stabilizing compound is diphenyldisulfide-Za,3'-dicarboxylic acid.

3. A light-sensitive silver halide emulsion as defined in claim 1 wherein the antifogging and stabilizing compound is diphenyldisulfide-2,2-dicarboxylic acid.

4. A light-sensitive silver halide emulsion as defined in claim 1 wherein the antifogging and stabilizing compound is diphenyldisulfide-4,4'-dicarboxylic acid.

5. A light-sensitive silver halide smulsion as defined in claim 1 wherein the vantifogging and stabilizing compound is present in the emulsion in a ratio of 0.02 to 20 mg. per 0.6 gram-mol of silver halide.

6. A light-sensitive silver halide emulsion as defined in claim 1 containing an optical sensitizer.

7. A light-sensitive silver halide emulsion as defined in claim 1 containing an accelerator.

8. A light-sensitive photographic element comprising a base and a coating of a gelatin-silver halide emulsion thereon, said emulsion containing as an antifogging and stabilizing agent a compound of the following general formula:

COOH

wherein the disulfide group occupies one of the positions ortho, meta and para to the carboxyl groups in each of the benzene rings.

9. A light-sensitive element as defined in claim 8 wherein the antifogging and stabilizing agent is diphenyldisulfide-3,3-dicarboxylic acid.

10. A light-sensitive element as defined in claim 8 wherein the antifogging and stabilizing agent is diphenyldisulfide-2,2'-dicarboxylic acid.

11. A light-sensitive element as defined in Claim 8 wherein the antifogging and stabilizing agent is diphenyl disulfide-4,4'-dicarboxylic acid.

12. A light-sensitive structure comprising a base, a layer of light-sensitive silver halide emulsion thereon and an adjacent layer separate from the first mentioned layer containing as an .antifogging and stabilizing agent a compound of the following general formula:

(IJOOH ([JOOH wherein the disulfide radical occupies one of the positions ortho, meta and para to the carboxyl group in each of the benzene rings.

15. A process of forming a light-sensitive photographic element having a reduced tendency to fog which comprises forming an emulsion, ripening said emulsion, coating said emulsion on a base and adding to the emulsion just prior to the coating thereof on the base a compound having the following general formula:

OOOH (300E wherein the disulfide radical occupies one of the positions ortho, meta and para to the carboxyl group in each of the benzene rings.

16. A process of minimizing and preventing fog in a light-sensitive silver halide material comprising a base having a light-sensitive emulsion therein, which comprises exposing said emulsion to light and developing the same in the presence of an antifoggant of the following general formula:

COOH COOH wherein the disulfide radical occupies one of the positions ortho, meta and para to the carboxyl group in each of the benzene rings.

17. A process of minimizing and preventing fog in a light-sensitive silver halide material as defined in claim 16, wherein said antifoggant is diphenyldisulfide-3,3'-dicarboxylic acid.

18. A process of minimizing and preventing fog in a 6 light-sensitive silver halide material as defined in claim 16, wherein said antifoggant is diphenyldisulfide-2,2-dicarboxylic acid.

19. A process of minimizing and preventing fog in a light-sensitive silver halide material as defined in claim 16, wherein said antifoggant is diphenyldisulfide-4,4-dicarboxylic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,440,110 4/1948 Mueller 96109 3,062,654 11/1962 Allen et al 96109 OTHER REFERENCES Beilstein: Handbuch der Organischen Chemie, 4th Ed., vol. X, p. 129 (1927).

NORMAN G. TORCHIN, Primary Examiner. 

1. A LIGHT-SENSITIVE SILVER HALIDE EMULSION CONTAINING AS AN ANTIFOGGING AND STABILIZING AGENT A COMPOUND OF THE FOLLOWING GENERAL FORMULA: 